For Peer Review - Wireless Power Transfer for Electric ...wireless.uga.edu/EVWCReview Submission.pdfcorrectly, this power transfer method, known as inductive power transfer, typically

For Peer Review

Electric Vehicle Wireless Charging Technology: A State-of-

the-art Review

Journal: Wireless Power Transfer

Manuscript ID: WPT-REV-14-004

Manuscript Type: Review Articles

Date Submitted by the Author: 17-Mar-2014

Complete List of Authors: Fisher, Taylor; The University of Georgia, College of Engineering Tse, Zion; The University of Georgia , Engineering Farley, Kathleen; Southern Company Services, Inc., Research

Keywords: Electric Vehicle, Wireless Charging, Inductive Charging, Magnetic Resonance, Wireless Power Transfer

Cambridge University Press

Wireless Power Transfer

For Peer Review

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Electric Vehicle Wireless Charging

Technology: A State-of-the-art Review

Taylor M. Fisher1, Kathleen Blair Farley

2, Yabiao Gao

1, Hua Bai

3, Zion Tsz Ho Tse

1

1Medical Robotics Laboratory, College of Engineering, The University of Georgia

2Southern Company Services, Inc.

3Advanced Power Electronics Lab, Electrical & Computing Engineering, Kettering University

Electric Vehicles (EVs) are becoming more popular due to concerns about the environment

and rising gasoline prices. However, the charging infrastructure is lacking, and most people

can only charge their EVs at home if they remember to plug in their cars. Using the principles

of magnetic inductance and magnetic resonance, Wireless Charging (WC) could help

significantly with these infrastructure problems by making charging secure and convenient.

WC systems also have the potential to provide dynamic charging, making long road trips with

EVs feasible and eliminating range anxiety. In this paper, we review companies that have

developed Electric Vehicle Wireless Charging (EVWC) systems, automobile manufacturers

interested in such technology, and research from universities and labs on the topic. While the

field is still very young, there are many promising technologies available today. Some systems

have already been in use for years, recharging public transit buses at bus stops. Safety and

regulations are also discussed.

Corresponding author: Zion Tsz Ho Tse; email: [email protected]; phone: +1 706 542 3030

Key words: Electric Vehicle, Wireless Charging, Inductive Charging, Magnetic Resonance,


I. INTRODUCTION Electric Vehicle Wireless Charging (EVWC) technology operates on the principles of magnetic

inductance and magnetic resonance. Similar to the way a transformer operates, a magnetic field

is induced in the surrounding area by running currents through a coil of wire. Exposing another

coil nearby to that magnetic field will induce an electric current in the nearby coil; thus, Wireless

Power Transfer (WPT) is achieved. However, unless the coils are very close together and aligned

correctly, this power transfer method, known as inductive power transfer, typically has a

suboptimal efficiency [1, 2].

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To increase the WPT efficiency at longer distances between the source and the receiver with

poor alignment, magnetic resonance is introduced [2-6]. This involves “tuning” the source and

receiver circuits so that they both magnetically resonate at the same frequency, which greatly

improves WPT efficiency. Some research has demonstrated that optimizing shape, arrangement

and number of the turns in the transmission and receiver coils can increase the WPT efficiency

[7, 8]. In addition, a number of specialized circuits are required to convert the AC signal to DC

in order to charge the battery, as well as to regulate voltage and current levels that can greatly

fluctuate depending on the alignment of the coils [9].

In the past decade, EVs have gained popularity due to concerns about the polluting the

environment with greenhouse gases and a desire to move toward “greener” energy [10, 11].

However, plug-in EVs have their problems: they require the user to change his or her behavior

by remembering to plug in the EV, and their charging infrastructure (public charging stations) is

vulnerable to weather (rain, snow, ice) and vandalism (stealing the cord, blocking the outlet).

The cord can pose a trip hazard, and due to the large amount of power being transferred, it also

carries the risk of electrocution [12].

Wireless Charging (WC) technology for EVs may improve upon EV convenience and related

infrastructure as well as charging safety. EVs that are charged wirelessly are easy to use – the

user simply parks the EV and allows it to charge. WC infrastructure can be buried or built into

the ground and completely sealed with no outlets, making it inherently safe from weather,

vandalism, and electrocution hazards. Well-distributed WC facilities available for EV charging

could allow more frequent charging and shorten the charging time required. Infrastructure

allowing EV users to “park and charge” their vehicles virtually everywhere may lead to battery

size reductions and lightweight EV designs.

With stationary wireless charging, the user simply parks the vehicle over a charging pad on the

floor, and a corresponding charging pad mounted on the underside of the vehicle picks up the

signal and charges the vehicle. Similar WC technology has already been applied in public

transportation systems at bus stops in what is known as “opportunity charging”. When the bus

idles at a bus stop, charging coils embedded in the road charge the bus for as long as it remains at

the stop. This system has allowed electric city buses to reduce their battery sizes, thus making the

buses more efficient by reducing their weight. Similar technology could also reduce the size of

the heavy batteries carried by electric cars and other vehicles.

WC technology could further be used for dynamic wireless charging, i.e. charging while the

vehicle is moving. Usually, dynamic WC concepts involve a single charging pad or a string of

charging pads that are built into the road or highway, and each charging pad is activated for a

split second as the car passes over it [13-15]. Charging a vehicle while it travels on the highway

would mean that an EV user would not have to make stops to recharge during extended road

trips. A designated WC lane for EVs on highways could sustain EVs for hours, eliminating range

anxiety.

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This paper endeavors to review the available and developing WC technologies for EVs from EV

charging technology companies, from car manufacturers and from universities and research

institutes.

II. WIRELESS EV CHARGING TECHNOLOGY COMPANIES There are a few major players in the EVWC field, including WiTricity, Qualcomm, Conductix-

Wampfler, Bombardier, EVWireless, and Momentum Dynamics. WiTricity is a start-up in

Watertown, MA that began at the Massachusetts Institute of Technology. Their commercialized

EVWC technology involves receiver and transmitter charging pads that operate on wireless

power transfer via strongly coupled magnetic resonances (WiTricity) [15]. The receiver pad

attaches to the bottom of the car, and the transmitter pad stays on the garage floor or is embedded

in a paved parking spot, as shown in Fig. 1a [15, 16]. This system incorporates a source driving

coil, two well-tuned resonance coils and a receiver-driving coil. The two resonance coils, in spite

of their relatively low coupling factor due to their separation, are tuned to resonate at the same

frequency [17, 18] so that energy can be transferred over a distance. Coupling factor is referred

to the magnetic interference between the Transmission (Tx) and Receiving (Rx) coils. Tuning the

two circuits’ resonance frequencies and matching their impedances greatly increases efficiency

and decreases power losses from the system. WiTricity’s system has an efficiency of about 90%

and a power transfer rate of up to 3.3 kW [16, 19, 20]. Energy transfer can occur through any

non-metallic surface, meaning that the floor pad can be installed below a garage floor or

embedded in pavement. Its operating frequency is about 145 kHz, and its lateral position

tolerances are ±20 cm side-to-side and ±10 cm bumper-to-bumper [16].

Qualcomm’s Halo group has developed stationary WC pads in collaboration with the University

of Auckland [21]. Their patented “Double D” magnetic polarized pads (Fig. 1b), are claimed to

have a unique arrangement that delivers twice the power with a higher efficiency compared to

circular pads (Fig. 1c) [21]. Qualcomm is still in the process of investigating the best charging

frequency to use for their EVWC devices, but uses 20 kHz as their frequency of choice in their

HaloIPT system as of 2012 [9]. In 2011, Qualcomm announced that their pads were scheduled to

undergo a trial run in East London’s Tech City [22]. In the future, Qualcomm hopes to develop a

dynamically charging system that would power motors directly as users drive. This would

increase efficiency dramatically, since charging the battery rather than the motor itself introduces

power losses of about 15% [21].

(a) WiTricity’s wireless charging

pads

(b) Double DD coil design

from Qualcomm’s Halo

(c) Circular coil design

Fig. 1: (a) WiTricity’s highly resonant wireless charging pads for electric vehicles [16]. (b)

Qualcomm Halo’s patented “Double D” coil design as compared to (c) a traditional circular coil

design (left) [21].

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Conductix-Wampfler’s inductive WC system has already been operating in electric buses in

Torino, Italy for the past 10 years [23]. Their system consists of a primary (stationary) side,

which is installed on the road, and a secondary (vehicle) side, which uses one or more pickups

and rectifiers. As shown in Fig. 2, energy is delivered from a track supply through the primary

coil to a battery bank. Conductix-Wampfler tunes the resonant frequency of each system

individually, and has achieved over 90% efficiency at a separation distance of 4 cm with 60 kW

power transfer [23].

Fig. 2: Conductix-Wampfler’s wireless charging system schematic [24].

Bombardier’s PRIMOVE system addresses both the static and the dynamic charging needs of

buses, cars, and even light rail systems [25]. Currently, Bombardier’s dynamic charging has only

been applied to light rail systems, using single charging pads built into the track; however, it

could be adapted for use with road vehicles. The system’s roadside components for buses

include: primary coils which provide the inductive magnetic field; shielding to prevent

electromagnetic interference; a Vehicle Detection and Segment Control (VDSC) cable that

identifies PRIMOVE vehicles above the system; a Supervisory Control and Data Acquisition

(SCADA) interface which supplies information for system control and diagnostics; and inverter

and power supply cables. The onboard vehicle components include a power receiver system of

pickup cables and a compensation condenser, inverters, a battery, and a VDSC antenna. Their

system is currently being used in public transportation by buses in Braunschweig, Germany [26].

EVWireless has developed EV wireless chargers that use Pulse Transmission Nanocomposite

Magnetic Coupling (PTNMC) technology [27]. In spite of lacking publication references, their

website claims that the pulse transmission mechanism can effectively control the switching

frequency and charging duty cycle on demand, allowing electrical energy to be supplied

intermittently at high voltage and high frequency with great efficiency. They also claim that the

use of nanocomposite carbon-copper coil designs improves efficiency due to improved signal-to-

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noise ratio properties of the material. In addition, they claim that their device, a 420mm diameter

pad, will address both stationary and dynamic WC needs.

Momentum Dynamics has developed a product using magnetic induction in much the same way

that the other companies’ devices do [28]. They have also developed software that would enable

energy suppliers to collect money from those who use their system to charge their EVs in a

manner similar to Automatic Toll Collection Systems. Their system can rapidly charge

commercial vehicles using a power system that supplies 240 Volts through air gaps of up to 24

inches. It is claimed that their system can achieve 92% efficiency rates [15]. Their founder and

CEO, Andy Daga, stated that the product can currently transfer 3.3 kW of power, and that

upgrades to 7.2 kW and then to 10 kW were planned. With these upgrades, the system could

charge a car such as the Chevy Volt in approximately one hour [29]. Momentum Dynamics’

systems are currently being implemented in select FedEx trucks from Smith EVs. Table 1

summarizes commercialized EVWC technologies and their specifications.

HEVO Power is another company who is implementing static and dynamic wireless charging

zones (green parking zones) for city EV owners, aiming to reduce the costs and emissions.

Table 1: EVWC Companies

Company Operating

Frequency

Power

Transferred

Separation

Distance

Efficiency

WiTricity [15, 16] 145 kHz 3.3 kW 18 cm 90%

Qualcomm Halo [9, 21] 20 kHz 7 kW N/A N/A

Conductix-Wampfler [23] N/A 60 kW – 180 kW 4 cm >90%

Bombardier [25] N/A N/A N/A N/A

Momentum Dynamics [15, 29] N/A 3.3 kW – 10 kW 61 cm 92%

III. AUTOMOBILE COMPANIES ABDOPTING EVWC TECHNOLOGY Several automobile companies are developing WC technology or are working with other

companies to develop WC technology. Delphi, Inc. has partnered with WiTricity to make use of

WiTricity’s unique stationary charging technology [30]. Likewise, Toyota, Mitsubishi, and Audi

have also shown interest in WiTricity’s WC technology [31].

Plugless Power devices, manufactured by Evatran LLC, are available for the Nissan Leaf and the

Chevy Volt [32]. This technology addresses stationary charging needs for home users.

Reportedly, BMW and Nissan are developing WC technology for EVs [33]. BMW is working

with Siemens Corporation on an inductive charging system, with trials that were supposed to

begin in June of 2011 in Berlin [34]. Nissan is developing a WC system for its 2015 Infiniti LE

four-door luxury electric car with an automatic parking system to ensure the car is parked

directly over the charging pad [35].

Daimler, Audi, Opel, BMW, and Volkswagen are all participating in a project sponsored by the

German government, the goal being to create a house that generates more electricity than it

consumes [36]. The house is designed to be energy efficient and is equipped with energy

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management technology. It uses photovoltaic cells to generate electricity, and any excess energy

it generates will be stored in batteries to charge EVs. Each automaker donated one EV to the

cause for a period of 3 months to be charged with stationary WC pads in the house’s garage.

Daimler was the first to donate a car in March 2012; they donated a Mercedes-Benz A-Class E-

CELL with an inductive WC system added as a modification.

IV. EVWC RESEARCH STUDIES

At Korea Advanced Institute of Science and Technology (KAIST), Jin Huh et al worked on a

project known as On-Line Electric Vehicles (OLEV), in which they designed four stages of

wirelessly charged EVs that draw power from an electrically charged road grid [10]. In the first

phase, they transferred approximately 3kW output power across an EV air gap of 1cm at an

efficiency of about 80%. Their second phase involves an EV with an ultra-slim U-type mono

rail, which yields 52 kW output power and produces an efficiency of 72%. The second stage’s air

gap jumped from the 1 cm to 17 cm. One of KAIST’s third generation OLEVs is a Sport Utility

Vehicle (SUV) with an ultra-slim W-type rail that operates with 71% efficiency at the same 17

cm air gap, obtaining 15 kW per EV operating on the mono rail. KAIST also made a third-

generation bus with an improved efficiency of 83% and a 20cm air gap, as well as a train with

74% efficiency and a 12 cm air gap. KAIST is currently working on a fourth-generation bus with

underground narrow power rails [10].

A spin-off company from Utah State University called Wireless Advance Vehicle Electrification

(WAVE) has developed an electric transit bus that is charged wirelessly [37]. Charging pads

embedded in the concrete roadways at strategic locations charge the electric bus via magnetic

induction. It currently operates at 25 kW, but the company plans to upgrade to 50 kW by mid-

2013 [15]. The buses are intended to serve the University of Utah campus, but the company still

needs to ensure the wireless charging pads will not interfere with someone’s pacemaker should a

person fall chest-first onto the charging pad. The system provides an 85% battery weight savings

for the electric bus over conventional EV battery packs.

Oak Ridge National Laboratory (ORNL) has developed an EVWC system that could be used

statically or dynamically [38]. The ORNL discovered that operating frequency set at 50 – 95% of

the resonant frequency can result in optimal power transmission efficiency. Their system uses a

transformer with an air core, which is loosely coupled to the storage battery. The ORNL system

also enhances the system’s efficiency by using a coupling coil as well as carbon nanotube or

graphene wire coatings [38]. A schematic of ORNL’s system is found in Fig. 3.

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Fig. 3: Oak Ridge National Laboratory’s EVWC system [38].

The University of Auckland partnered with Daifuku and Conductix-Wampfler to develop an

inductive EVWC system for a monorail device, and later for electric road vehicles [39]. Their

system uses inductive power transfer and has been tested at 1.5 kW with a 4 cm air gap. A

diagram of their power pad design is shown in Fig. 4a. The design may be used someday as a

dynamic charging lane with long series of these charging pads to charge vehicles on long trips,

as depicted in Fig. 4b.

(a) Power pad diagram (b) Vision for future dynamic use of power charging pads

Fig. 4: Diagram and vision of the power pad design from the University of Auckland [14].

A study on different geometries of coils for wireless power transfer using electromagnetic waves

was done by Horiuchi and Kawashima at Setsunan University [40]. The shapes of horn, patch,

and array antenna coils were respectively. While the horn-shaped antennas are the most efficient,

this shape is rather impractical for electric vehicles because of its 3-dimensional nature. The

patch antenna is a more practical shape for electric vehicles because it is planar in nature, but its

efficiency was lower than the horn antenna. Reducing the patch antenna frequency from 2.45

GHz to 1.20 GHz greatly reduced the transmission loss; the array antenna at the 2.45 GHz

frequency also showed reduced transmission loss compared to the patch antenna at the same

frequency.

At Tokohu University, research was done on the Tx-Rx coupling factor and efficiency when the

gap between coils was changed, using a basic Resistive-Inductive (RL) circuit and Resistive-

Inductive-Capacitive (RLC) circuit booster on the receiving side [41]. They found that the larger

the gap, the lower the efficiency and coupling factor.

Wu et al at Utah State University reported on their designed 5 kW inductive charging design for

EVs [42]. They have achieved 90% and higher efficiency levels with their system under full

loads, and this efficiency can even be increased by 7% at light loads. The system meets the

stringent international safety requirements for medical device interference (such as pacemakers)

and other important electronic equipment.

The University of Tokyo studied the feasibility of an EVWC system based on magnetic

resonance [43]. They discovered that while the transmission and receiving coils with large air

gaps couple weakly by using magnetic resonance, they could still transfer energy at a high

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efficiency. The paper also mentions WiTricity, the spin-off from MIT that uses magnetic

resonances to transfer power in a strongly coupled frequency range on the order of megahertz

[6]. WiTricity was able to transfer power over 2 meter gaps with about 40% efficiency. This

efficiency improved as the air gap was closed (Fig. 5). Researchers at the University of Tokyo

also described a new technique for EVWC using near-field coils at resonance [44]. This

technique can transfer power with high efficiency over large air gaps, making it ideal for EVs;

however, it is still being optimized.

Fig. 5: WiTricity’s theoretical predictions and experimental results for power transfer efficiency

as a function of the distance between the coupled coils [6].

The researchers at the University of Tokyo also reported that when power is transferred via

magnetic resonance coupling, impedance matching tuning circuits can help optimize the

efficiency of power transfer and minimize reflection [45]. Fig. 6a shows a schematic of their

RLC circuits. As shown in Fig. 6b, the transfer and reflection ratios form two peaks at smaller

gap distances, and as the distance increases, the two peaks merge into one. At much higher gap

distances, the single peak drops down and the maximum transfer efficiency decreases. An

impedance matching circuit controlled by a computer was used to tune the resonant frequency of

the system to match the power source (around 13.56 MHz). As a result, the power transmission

efficiency greatly increased (Fig. 6c).

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Fig. 7 shows a typical wireless charging topology [46], which contains the AC/DC portion using

interleaving topology and the DC/DC portion employing full-bridge resonant topology. Half-

bridge resonance is another choice, depending on the input and output voltage. Here two coils,

LP, LS, CS and CP, form the resonance network. Other types of resonant networks could also be

utilized as well [46].

AC

L

S1 S2

D5 D6

Lp Ls

Vb

Rb

S3

S4

D1

D2

20cm

DC/DCAC/DC

Cs

S5

S6

Cp

(a) Circuit schematic (b) Frequency versus transmission and

reflection coefficient

Air gap = 100 mm

Air gap = 200 mm (Optimal Distance)

n21: transmission coefficient

n11: reflection coefficient

(n21)2 x 100%: transmission power efficiency

(n11)2 x 100%: reflection power efficiency

(c) Experimental effects of impedance matching on the frequency versus efficiency

Fig. 6: The University of Tokyo’s WC system (a) circuit schematic, (b) frequency versus power

transmission (%21) and reflection (%11) ratios for different gap lengths and (c) experimental

effects of the impedance matching circuit on the frequency versus efficiency graph at a gap of

13 cm [45].

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Fig. 7: Proposed wireless charging circuit [46].

The CoolMOS MOSFET was adopted [46] due to its low internal resistance and thereby low on-

state loss. Its major demerit is the poor performance of its body diode, which usually has high

reverse recovery loss in the hard turn-off mode, not only leading to low system efficiency but

also creating significant electromagnetic interference (EMI). Therefore in most high-efficiency

battery chargers, softly turning on the CoolMOS, i.e., softly turning off its body diode, is

preferable. Fig. 8 displays the MOSFET voltage VDS (blue) and current ID (red). It indicates

that right before the MOSFET turns on, the current flowing through the MOSFET is still

negative, i.e., flowing through its body diode. After the MOSFET turns on, the current

commutates from its body diode to the MOSFET channel, i.e., softly turning on. When the

current polarity is reversed, the MOSFET body diode is naturally turned off without any reverse

recovery loss. This commutation process realizes zero voltage switching (ZVS).

Fig. 8: Soft switching of the MOSFETs in the DC/DC portion (VDS- Blue, ID-red) [47].

The AC/DC portion also needs high efficiency (>97%) operation and a high power factor

(>0.99). The topology adopted in Fig. 8 is an interleaving circuit, which needs a much smaller

inductance compared to other AC/DC circuits. It can also realize ZVS of S1 and S2. Here, the

gate signals of S1 and S3 have a 180° phase difference, with each leg undertaking half of the

overall power. The interleaved number will vary based on the input type, i.e., single phase or

three phase [47]. The interleaved topology is essentially a unidirectional converter. If

bidirectional power flow is required, the full-bridge topology can be utilized [48].

Saitama University has partnered with Technova, Inc. and Aisin AW Co. Ltd., in Japan, to

produce a device that has a double-sided winding with novel H-shaped cores, as shown in Fig. 9

[49]. Compared to a rectangular core, the H-shaped ferrite core decreases the weight of the

transformer, reduces copper losses due to shorter windings, and enhances tolerance to lateral

misalignment due to the increased length of the magnetic poles in the lateral direction. The

design also includes an aluminum sheet attached to the back of the pick-up coil to prevent

leakage flux. At an air gap of 7 cm and power transfer rate of 1.5 kW – 3.0 kW, the device has an

average efficiency of around 94%.

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Fig. 9: Saitama University’s double-winded WC device with a unique H-shaped ferrite core [49].

One unique system designed and in use at the University of British Columbia (UBC) does not

use resonant inductive wireless power transfer. Instead, it uses a set of magnetic gears, an electric

motor, and an electric generator to transfer power [50]. The electric motor is mounted on the

ground and rotates a magnetic gear, that is coupled to a magnetic gear onboard a car (Fig. 10).

The coupled magnetic gear turns the generator onboard the car, generating electricity, which is

stored in the car battery. The system operates at a significantly lower frequency than typical

resonant and inductive systems, around 150 Hz, and achieves an efficiency of around 81%. It

transfers 1.6 kW of power over a distance of 15 cm. The system is currently used to charge EVs

when they are parked on the UBC campus.

Fig. 10: A photo of the University of British Columbia’s magnetic gear WC device [50].

Table 2 contains a list of the above reviewed research work and the various specifications

for each system developed.

Table 2: EVWC Research

University/

Institution

Operating

Frequency

Power

Transferred

Separation

Distance

Efficiency

KAIST [10] 20 kHz 3 kW - 52 kW 1 cm – 20 cm 71% - 83%

Utah State University

(WAVE) [15, 37] N/A

25 kW – 50

kW 15 cm > 90%

ORNL [38] N/A > 4 kW 25.4 cm 92%

University of Auckland

[39] N/A 1.5 kW 4 cm N/A

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V. SAFETY & REGULATIONS

All the above breakthroughs in EVWC technology are of limited usefulness to the EV market if

they cannot be made safe for human contact and interaction. Researchers developing EVWC

systems should also check the safety of their systems and make sure that their WC devices

conform to safety standards. The “Standard for Safety Levels With Respect to Human Exposure

to Radio Frequency Electromagnetic Fields, 3 kHz to 300 GHz” is made by the Institute of

Electrical and Electronic Engineers (IEEE) [51]. Guidelines for limiting exposure to time-

varying electric, magnetic, and electromagnetic fields (up to 300 GHz) are made by the

International Commission on Non-Ionizing Radiation Protection (ICNIRP) [52]. In the United

States, safety standards are governed by the Federal Communications Commission (FCC) [53].

These standards are set to protect humans from the adverse health effects caused by

electromagnetic radiation from man-made devices.

Both the IEEE and the ICNIRP have determined that there is no strong evidence that exposure to

electromagnetic fields causes cancer. However, other adverse health effects are possible,

including tissue heating as well as nerve and muscle stimulation. Retinal phosphene visualization

is another possible effect; that is, electromagnetic waves can induce the sensation of light in the

retina without light actually being present. These effects should all be considered when

determining standards. The current standard all three organizations agree upon for tissue heating

is set at a specific absorption rate (SAR) of 0.08 W/kg for the general public for a long term

environmental exposure, and set at a SAR of 4 W/kg for a short term exposure (1st level

controlled), which is equivalent to a maximum of 1°C rise in the body temperature [47, 51, 52].

Nerve and muscle stimulation, including retinal phosphenes, do not have any direct or lasting

adverse health effects; however, all three standard-setting organizations have decided these

effects should be avoided. The internal electric field limit set by the IEEE depends on the part of

the body exposed, and ranges from 2.1 x 10-4

x f V/m to 6.3 x 10-4

x f V/m, where f is the

electromagnetic field frequency in Hz. The ICNIRP recommends a slightly lower field limit of

1.35 x 10-4

x f V/m. Computation simulations and experimental measurements are possible

methods to study the electric field and specific absorption rate of a human body standing near a

charging car.

VI. CONCLUSION

Setsunan University [40] 1.20 GHz –

2.45 GHz N/A 5 cm – 25 cm 20% - 98%

Tokohu University [41] 360 kHz 15 W – 18 W 0 cm – 200 cm 75%

Utah State University [42] N/A 5 kW N/A 90% - 97%

University of Tokyo/

WiTricity [6, 43-45] 13.56 MHz 60 W 5 cm – 200 cm 40% - 90%

Saitama University [49] 30 kHz 1.5 W – 3.0 W 7 cm 94%

University of British

Columbia [50] 150 Hz 1.6 kW 15 cm 81%

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EVWC technology is growing quickly and moving forward. Charging systems are starting to

become commercially available as the EV market slowly grows, and the improved infrastructure

is bound to boost the popularity of EVs. Further developments are increasing EVWC efficiency,

and many players in the EVWC field are competing for space in the newly formed market niche.

The many uses of EVWC include stationary applications such as home garages, public parking

spaces, and opportunity charging stations, while dynamic applications include highway-charging

lanes that would allow EVs to continuously drive on the highway for hours without stopping to

charge. Behind these applications, magnetic resonance and induction technologies are being

developed so that the efficiency of wireless charging can rival that of traditional plug-in

charging.

This paper has reviewed the solutions from a myriad of companies working on the EVWC

problem, including WiTricity, Qualcomm Halo, Conductix-Wampfler, Bombardier, EV Wireless

and Momentum Dynamics. We have also reviewed the car manufacturers interested in adopting

EVWC technology, including Delphi, Toyota, Mitsubishi, Audi, Nissan, Chevy, BMW, Daimler,

Opel, and VW. Finally, we have reviewed the technical research that has been done by

researchers at several universities and labs on the subject of EVWC technology, such as KAIST,

Utah State University, ORNL, the University of Tokyo, the University of Auckland, Setsunan

University, Tokohu University, Saitama University and the University of British Columbia.

Safety and regulations have also been discussed. EVWC technology is still in its infancy, but it

promises to change the world of EVs for the better.

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For Peer Review - Wireless Power Transfer for Electric ...wireless.uga.edu/EVWCReview Submission.pdfcorrectly, this power transfer method, known as inductive power transfer, typically